In a conventional method of mounting integrated circuits, wire bonds are made from bonding pads on the chip to terminals mounted in a package. Terminal pins projecting from the package are mounted within holes in a printed circuit board. The board provides physical support for the chip package and the printed circuit electrically connects the chip to other components in an electronic circuit.
In an alternative packaging technology called the "flip chip" technique, the chip is inverted so that bonding pads on the chip surface face downwardly towards the substrate and corresponding bonding pads are formed on the upper surface of the substrate. Solder bridges are made between the bonding pads on the chip and bonding pads on the substrate to afford both mechanical and electrical connection.
In these known packaging techniques, it is known to coat the exposed upper surface of the chip with a layer of dielectric such as phosphosilicate glass (PSG). The phosphosilicate glass acts to protect the chip from corrosion and ionic contamination by materials which can alter the performance of the circuit.
A problem with high frequency circuits is that an overlying protective dielectric layer can increase the capacitance of aluminum conductors at the chip surface. To reduce the capacitance it is known to fabricate a hermetically sealed integrated circuit package in which an air space exists between the top layer conductor and a protective cap positioned over the integrated circuit chip.
A modification of the flip-chip packaging method particularly adapted for high frequency circuits is now proposed.